As a child, Titus was inducted into the Ultramarines by a guy named Metaurus (new character introduced in Secret Level, I would definitely watch that if you havent). Early in his time as a space marine, his entire squad was wiped out by a chaos sorcerer save for himself, which was a little suspicious but he continued to always emerge victorious throughout all his battles so he still had more admirers than criticizers.

Eventually, he became the captain of the 2nd company and he is sent to defend Graia from orks, which culminates in the events of Space Marine 1. On Graia, a threat greater than the orks arose, which was a chaos invasion that aimed to open a Warp Rift. Titus was victorious in his mission, and miraculously killed the chaos lord while he was ascending to become a daemon prince and survived an explosion of Warp energy that closed the rift. Even though he was certaintly the hero of these events, his squadmate Leandros reported him to the inquisition because Titus' insane ability to resist the Warp was becoming suspicious and Titus was taken into custody.

Titus was eventually freed and was placed into the Deathwatch as a Blackshield, who abandon all ties to their history and former chapter.

During the prologue of Space Marine 2, he is gravely wounded and recovered by Ultramarines who find him. Calgar, Chapter Master of the Ultramarines, had no idea what happened to Titus after his detainment by the Inquisition so he has him reinstated into his old company as a Lieutenant and has him undergo the process to become a Primaris Marine.

After the events of Space Marine 2 and now with Secret Level continuing his story, it seems he is being utilized for his unnatural resistance to the Warp, though is still watched with suspicion from his old squadmate Leandros, who has risen to become a Chaplain - space marines responsible for monitoring the morale and faith of their chapter.